[Translator’s note: the sweetness of miso is determined by the ratio of koji (starch/sugar) to beans (protein)—the larger the amount of koji, the sweeter the resulting miso.]

Sweet miso: soybeans 1100g, koji 2600g, salt 750g

Medium sweet: soybeans 1300g, koji 2000g, salt 800g

Dry miso: soybeans 1500g, koji 1800g, salt 800g

[The above figures for koji is for fresh koji. If using dry koji, decrease the amount by 20%—1800 grams instead of 2000, for example. Then add the same amount of water (200cc in the example) to koji to reconstitute it.]

This is the original recipe that has been passed down through generations at Marukawa Miso. It has a larger amount of koji compared to other commercial products, resulting in sweeter miso.

Step 1: Soybeans—the Key Ingredient

The most important step in miso-making is cooking of beans. How the beans are cooked determines the color, flavor, fragrance, and texture of the finished miso.

What to Look For in Soybeans

Choose large beans

Beans from current year (readily absorb water)

Beans with good flavor

The better the cooked beans taste, the better the miso will be.

Wash beans thoroughly and soak in water three times the weight of the beans for 18 hours. It is imperative that the beans are fully hydrated. Check by splitting one bean in half. If the center is still hard (left in photo), soak longer.

Step 2: Cook soybeans

Discard water (beans are surprisingly dirty—if cooked in soaked water, the color turns slightly grayish), fill the pot with fresh water until the beans are just covered, turn on heat to high.

When the water first comes to boil, add a cupful of cold water. After it returns to boil again, turn the heat down to simmer and cook for 3 hours, adding water as needed so the beans are always covered.

If using pressure cooker, cook for 20 minutes.

Beans are fully cooked when you can crush a bean between a thumb and pinky finger, or at around 500g when pressed against a scale.

Don’t be concerned if you see skins of the beans floating in water. They can be mashed with the beans. But it may indicate over cooking—keep at a simmer to prevent this.

Step 3: Mash beans

Drain the beans, reserving some cooking liquid. Process the beans while hot until smooth, or mash them in a mortar and pestle or in a plastic bag with a glass bottle or rolling pin. This takes time when making a large batch.

Step 4: Mix ingredients

Mix rice koji evenly with salt in a big bowl or tub. Stir into mashed beans, mixing them all evenly. If using fresh koji and the beans are hydrated and cooked fully, no additional water should be necessary. If using dry koji, you could add some cooking water. Finished paste should have the feel of earlobe. Be careful not to add too much water in this step. This could cause mold to develop.

Step 5: Pack

Roll the paste into balls. Smash or press into a container. This could be a food grade plastic pail, ceramic crock, or a wooden tub. Press each ball firmly to eliminate air bubbles. Smooth the surface, place a parchment disk, paper, or plastic film directly on the miso, seal the edge, cover with a plate or wooden disk and weight it down with a stone or a large water bottle.

Step 6: Store

Cover with a towel, a lid with an airlock, or a loose lid. Store in a dark place with as little temperature fluctuation as possible. At room temperature, miso will be ready in 10 months to a year. Miso is forgiving with temperature. If cool, it’ll take longer to ferment, if hot, shorter. But do not check the miso frequently. Every time it touches air, you’d be inviting mold.

Ideally, keep the miso at around 10ºc for 3-4 months, at around 20ºc for 3-4 months, then at 30ºc for 2 months.

At Marukawa, we believe that miso is at its peak flavor at 10 months to a year, but it can be aged longer. Move to refrigerator to slow down fermentation.

About Mold

It’s almost inevitable that you’ll find mold on the surface of miso. Do not be alarmed. Simply scrape it off. To prevent excess mold growth, seal the surface and do not let miso be exposed to air (but it also has to breathe so don’t cover it with air-tight lid). At Marukawa, we use special washi, handmade by a national treasure Ichibei Iwano. It is also important to weight down the miso sufficiently. This will bring up excess liquid to top, preventing the surface from coming in contact with air. This liquid is tamari, considered as liquid gold by many.